High frequency band pass filter with coupled surface mount transition

ABSTRACT

A high frequency band pass filter with a coupled surface mount transition is provided, including a filter substrate, circuit connection elements defining input and an output elements provided on a surface of the filter substrate, electronic filter components provided on the first surface of the filter substrate, and impedance matching structures provided on the first surface of the filter substrate between the electronic filter components and the respective input and output elements. Signal connection structures are provided on an opposed surface of the filter substrate, in locations that positionally correspond to respective positions of the input and output elements. The respective signal connection elements are capacitively coupled, through a thickness direction of the filter substrate, to a respective one of the input and output elements on the opposed surface of the filter substrate without the presence of any vertical conductive structures within the filter substrate at the input and the output elements.

FIELD OF THE INVENTION

The present invention relates in general to high frequency surfacemounted passive radio frequency (RF) and microwave devices. Inparticular, the present invention relates to a high frequency band passfilter (BPF) with a capacitive coupled surface mount transition thateliminates presence of and need for providing vertical conductivestructures between the functional layers of the filter located on onesurface of a filter substrate and the signal connection structurelocated on the opposed surface of the filter substrate, which isdirectly connected to a printed circuit board in a surface mountedapplication.

BACKGROUND OF THE INVENTION

The terms “surface mount” or “surface mounted” technology (SMT) are usedin the electronics industry to describe how electronic components anddevices are mounted onto a printed wire circuit board and how thesignal, power, and control lines, as may be required, are connected tothe subject device. In particular, the subject component or device isepoxied or soldered on top of the supporting circuit board, and thus,surface mounted thereon. Conventional surface mount technology typicallyinvolves the use of vertical metallic conductive structures to connectthe circuitry on the printed wire board up to the functional layer ofthe surface mounted device. On passive RF and microwave devices, such asa band pass filter, this connection is accomplished at the RF input andat the RF output of the device.

FIGS. 1A-1C illustrate an example, shown schematically, of aconventional band pass filter (BPF) 1 including a ceramic (e.g.,dielectric material) substrate 2 that is surface mounted via solder orepoxy, for example, to a surface of a printed wiring board (PWB) orprinted circuit board (PCB) according to known methods. The ceramicsubstrate 2 of the filter 1 has a first surface 2 a (i.e., top surface)on which the electronic components of the filter are formed by variousmethods known in the art, and an opposed second surface 2 b (i.e., abottom surface) that directly interfaces with the circuitry on thePWB/PCB (see e.g., FIG. 2). While the ceramic substrate 2 is shown as asubstantially rectangular body having four sides 2 c-2 f, it should beunderstood that the shape of the filter substrate 2 is not strictlylimited to the illustrated shape, and other suitable shapes known in theart can also be employed.

In the typical BPF 1 shown, the electronic components of the filterinclude an RF input 3A formed on the first surface 2 a proximate theside 2 c of the ceramic material layer 2. The RF input 3A is connectedto have physical and electrical ohmic (i.e., metal to metal) contactwith at least one of a plurality of vertical metallic conductivestructures, such as a metallized half-vias (castellations) 6A formed onthe surface 2 a and extending along the side 2 c through the thicknessdirection of the ceramic filter substrate 2, the central one of which isalso connected to have physical and electrical ohmic contact with thecorresponding signal connection structure 7A located on the opposedsecond surface 2 b of the filter substrate 2. In that manner, the signalconnection structure 7A is ohmically connected with the RF input 3A ofthe filter 1.

Similarly, the filter 1 also includes an RF output 3B formed on thefirst surface 2 a proximate the side 2 d of the ceramic material layer2. The RF output 3B is connected to have physical and electrical ohmiccontact with a vertical metallic conductive structure, such as ametallized half-vias (castellation) 6B formed on the surface 2 d andextending along the side 2 d through the thickness direction of theceramic filter substrate 2, a central one of which is also is connectedto have physical and electrical ohmic contact the corresponding signalconnection structure 7B located on the opposed second surface 2 b of thefilter substrate 2. In that manner, the signal connection structure 7Bis ohmically connected to the RF output 3B of the filter 1.

In between the respective RF input 3A and output 3B, a first impedancematching structure 4A, a plurality of filter sections (as shown, thereare four sections 5A-5D), and a second impedance matching structure 4Bare also provided, in that order. The impedance matching structures 4A,4B are known in the art and are device application specific, as oneskilled in the art can readily appreciate. These impedance matchingstructures are needed to ensure proper signal transmission between theRF input 3A and the filter sections 5A-D, and likewise, from the filtersections to the RF output 3B.

It should also be noted that in the prior art structure shown in FIG. 1,substantially the entire bottom surface 2 b of the filter substrate 2 iscovered by ground plane 9, with the exception of the signal connectionstructures 7A, 7B and the electrically insulating isolation areas 8A, 8Bsurrounding the respective signal connections 7A, 7B. It is particularlyimportant that continuous ground layer be provided at least in portionscorresponding to the footprint of the filter section(s) and proximatethe RF input/output couplings. In reality, the size constraints of theactual devices make it such that the whole second (bottom) surface ofthe substrate is essentially covered with the exceptions noted above.

There is a demand, however, to increase the pass band frequencies forsurface mounted band pass filters in view of particular applications,such as fixed and mobile Wireless Access, Point to Point, mm-Wavecommunications. This is due to consumer demand for increased data andthe subsequent bandwidth requirements of the related microwaveequipment.

At higher frequencies, however, such as those above 30 GHz, the presenceof vertical conductive structures (such as a metalized via hole, orcastellations 6A, 6B as shown in FIG. 1) causes undesirable side effectsby launching parasitic (spurious) modes (energy). That is, verticalconductor structures are particularly efficient with respect to couplingenergy into waveguide cavity modes (i.e., radiated fields represented byarrows E in the wave guide enclosure 11, as shown in FIG. 2) in the stopband frequency ranges of the filter, where the reflected energy resultsin high RF current in the vertical conductor structure and high magneticfields. As shown in FIG. 2, the band pass filter 1 inside the wave guideenclosure 11 is connected to the printed wiring board 10. However, thismechanism also launches energy which was originally in a quasi-TEM modetransmission lines (e.g. micro-strip or grounded co-planar waveguide)and instead couples some of that energy into transverse electric (TE) ortransverse magnetic (TM) waveguide modes. This creates a parallel pathfor the energy to bypass the filter, thus degrading the overall filterperformance. These spurious modes are clearly undesirable, and can, insome instances, effectively render the subject surface mount deviceinoperable.

Accordingly, it would be desirable, therefore, to provide a highfrequency band pass filter that is not subject to the drawbacksassociated with the prior art structures that include verticalconductive structures within the ceramic substrate at the input andoutput. In addition, eliminating the need for vertical conductivestructures would simplify the manufacturing process and reduce costs byeliminating machining and metallization materials needed to form thevertical conductive structures.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above-describeddrawbacks associated with the prior art.

According to one aspect of the present invention, a high frequencypassive RF device with a coupled surface mount transition is provided,wherein electromagnetic coupling between signal connection elements onone side of a device substrate and circuit connection elements on avertically opposed side of the device substrate form an RF signalconnection, and vertical conductive structures are excluded from inputand output structures thereof. According to one aspect of the presentinvention, the device is a band pass filter.

According to another aspect of the present invention, a package for ahigh frequency active RF device with a coupled surface mount transitionis provided, wherein electromagnetic coupling between RF signalconnection elements on one side of an active device substrate and RFinput and output structures on a vertically opposed side of the activedevice substrate form an RF signal connection, and vertical conductivestructures are excluded from the active device in connection with the RFinput and output structures.

According to another aspect of the present invention, a high frequencyband pass filter with a coupled surface mount transition is provided,comprising a dielectric filter substrate having a first surface and anopposed second surface, circuit connection elements defining an inputelement and an output element provided on the first surface of thefilter substrate and spaced a distance d from respective terminal edgesof the first surface of the filter substrate, and electronic filtercomponents provided on the first surface of the filter substrate.Impedance matching structures are also provided on the first surface ofthe filter substrate and interposed between the input element and theelectronic filter structures and between the output element and theelectronic filter components, and signal connection elements areprovided on the second surface of the filter substrate in locations thatpositionally correspond to respective positions of the input element andoutput element on the first surface of the filter substrate. The signalconnection elements are respectively separated from a ground plane onthe second surface of the filter substrate by an electrically insulatingisolation area, and are spaced a distance d₂ from respective terminaledges of the second surface of the filter substrate. The respectivesignal connection elements on the second surface of the filter substrateare capacitively coupled, through a thickness direction of the filtersubstrate, to a respective one of the input and output elements on thefirst surface of the filter substrate without the presence of anyvertical conductive structures within the filter substrate at thecircuit connection elements.

Preferably, the filter substrate comprises a ceramic material having adielectric constant in a range of 9-25. In addition, the input andoutput elements preferably have a width dimension w in a range of 0.254mm to 0.356 mm and a length dimension l in a range of 0.254 mm to 0.356mm, and the signal connection elements have a width dimension w₂ in arange of 0.356 mm to 0.457 mm and a length dimension l₂ in a range of0.304 mm to 0.406 mm. The distance d is preferably in a range of 0.00 mmto 0.127 mm, and the distance d₂ is preferably in a range of 0.00 mm to0.076 mm.

According to another aspect of the present invention, a high frequencyband pass filter with a coupled surface mount transition is provided,comprising a filter substrate, circuit connection elements defining aninput element and an output element provided on a first surface of thefilter substrate, and electronic filter components provided on the firstsurface of the filter substrate. Impedance matching structures areprovided on the first surface of the filter substrate between theelectronic filter components and the respective input and outputstructures, and signal connection elements are provided on an opposedsecond surface of the filter substrate, in locations that positionallycorrespond to respective positions of the input and output elements onthe first surface of the filter substrate. The respective signalconnection elements on the second surface of the filter substrate arecapacitively coupled, through a thickness direction of the filtersubstrate, to a respective one of the input and output elements on thefirst surface of the filter substrate without the presence of anyvertical conductive structures within the filter substrate at thecircuit connection elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the present invention makesreference to the accompanying drawings, in which:

FIGS. 1A-1C are a top schematic plan view, a bottom schematic plan viewand a schematic end view of a prior art band pass filter structure;

FIG. 2 is a schematic cross-sectional view of the prior art filter ofFIG. 1 inside a waveguide;

FIGS. 3A-3C are a top schematic plan view, a bottom schematic plan viewand a schematic end view, respectively, of a band pass filter structureaccording to the present invention;

FIG. 4 is an electrical schematic representation of the band bass filtershown in FIGS. 3A-3C;

FIGS. 5A-5C are a top schematic plan view, a bottom schematic plan viewand a schematic end view, respectively, of a working example of a 40.5to 44.5 GHz band pass filter according to the present invention, andFIG. 5D is a graphic representation of the insertion loss and returnloss results measured in connection with the working example; and

FIG. 6 is an electrical schematic representation a package for an activehigh frequency, narrow band device according to another aspect of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

A number of the components of the band pass filter 30 shown in FIGS.3A-3C and 5A-5C generally correspond to the components of the band passfilter 1 described above. Like reference numbers have been used todesignate like components, and repeat descriptions are omitted. Thedifferences between the prior art band pass filter structure 1 and theinventive structure 30 are discussed in detail below.

The present invention successfully eliminates the need for andimplementation of vertical conductive structures within the dielectricbody of the filter at the input and output signal connection elements.Instead, electromagnetic coupling between the signal connection elementon the backside of the ceramic filter substrate, which is attached tothe supporting printed wire hoard, and the coincident circuit connectionelements (input and output) on the top surface of the subject filterforms the RF signal connection. This is represented by the capacitor 40in FIG. 4. The filter topology may include any number of suitable highfrequency topologies. In the example shown in FIGS. 3A-3C and 4, an endcoupled, four section topology is illustrated. An impedance matchingstructure (i.e., 34A, 34B in FIG. 3A) is necessary to transform theimpedance of the filter, Zo, to the reference impedance of system, Zc.

The impedance matching structures provide the complex conjugateimpedance to cancel the capacitive reactance of the couplingcapacitance, thereby enabling maximum power transfer (and minimum signalreflections) thru the surface mounted filter. For example, a distributedelement circuit structure is employed between the capacitor (i.e., acoupling structure) and the body of the filter to match the impedance ofthe filter, Zo, to the impedance of the parent circuit board, Zc. Manyknown electronic components and distributed element techniques aresuitable to accomplish this. With no vertical conductive materialpresent, the launching of undesirable spurious waveguide modes isprevented. The fabrication of high frequency band pass filters, as wellas other high frequency passive RF devices, utilizing this approach issimplified (by elimination of the signal vias), and precision improved,which results greater consistency of RF performance.

The first impedance matching structure 34A, the filter sections (four asshown, 35A-35D) and the second impedance matching structure 34B,schematically shown in FIG. 3A, are interposed between the RF input 33Aand the RF output 33B, in that order. It should be noted, however, thatthe number of filter sections is not limited to the four shown, and thatfewer or additional sections can be employed. One skilled in the artwould appreciate that design considerations control the selection ofspecific filter components and related matching structures. The presentinvention enables the provision of a high frequency band pass filterwithout including conventional vertical conductive structures at theinput and output for surface mount applications, which has not beenachieved prior to the present invention, and therefore amelioratesand/or eliminates the aforementioned undesirable effects attributable tothe vertical conductive structures noted above.

The physical structure of the coupled surface mount device according tothe present invention and the requisite dimensions are determinedprimarily in connection with the requirement to mount an RF component toa printed, 50 Ohm transmission line that is printed on any number ofcommercially available circuit board materials. The predominantly usedPWBs for mm-Wave applications have approximate thicknesses in the rangeof 0.203 mm to 0.305 mm, with dielectric constants of 3.2 to 3.8. Asuitable 50 Ohm transmission line is achieved with a conductor,typically about 0.508 mm in width (e.g., a signal conductor). The groundstructures necessary to complete the 50 Ohm transmission line structureare positioned on the same surface of the printed wire board, typicallywithin about 0.203 mm to 0.254 mm.

As shown in FIGS. 3A-3C, the BPF 30 includes an RF signal inputstructure (hereinafter RF input) 33A on the first (i.e., upper) surface32 a of the filter substrate 32 proximate the side 32 c thereof. Asshown, the RF input 33A is spaced a distance d away from the terminal,peripheral edges of the upper surface 32 a and does not extend over theside 32 c. Similarly, an RF signal output structure (hereinafter RFoutput) 33B on the first (i.e., upper) surface 32 a of the filtersubstrate 32 proximate the side 32 d thereof is provided on the uppersurface 32 a of the filter substrate 32 proximate the side 32 d thereof,and is spaced a distance d away from the terminal, peripheral edges ofthe upper surface 32 a, and does not extend over the side 32 d. The RFinput and output 33A, 33B are made of any suitable high conductivitymaterial, examples of which include, but are not limited to copper, goldor silver. The material of the RF signal input and output structures isappropriately selected by those skilled in the art in view ofmanufacturing considerations and the desired performance characteristicsof the resultant microwave device.

Preferably, the RF input and RF output 33A, 33B have a length dimensionl, measured in FIG. 3A in a direction parallel to the longitudinalextension direction of the plane of the upper surface 32 a of thesubstrate 32, that is in a range of 0.254 mm to 0.356, and morepreferably 0.305 mm. A width dimension w of the RF input and RF output33A, 33B, measured in FIG. 3A in a direction perpendicular to the lengthdirection 1, and also in the plane of the upper surface of the substrate32 a, is preferably in a range of 0.254 mm to 0.356, and more preferably0.305 mm. The RF inputs and RF output 33A, 33B are preferably spaced adistance from and do not extend over the respective sides 32 c, 32 d ofthe filter substrate 32. For example, the distance d between theterminal, peripheral edges of the upper surface 32 a of the filtersubstrate proximate the sides 32 c and 32 d and the respective RF inputand RF output 33A, 33B is in a range of 0.00 mm to 0.127, and preferably0.102 mm. Unlike the prior art structure shown in FIG. 1, the inventiveband pass filter 30 does not include any vertical conductive structuresextending over the substrate edge or passing or through the thicknessdirection of the filter substrate 32 associated with either the RF inputor RF output structures 33A, 33B.

The bottom surface 32 b of the filter substrate 32 is different from theprior art, and includes conducting pad structures (i.e., signalconnection structures 37A, 37B), which are preferably square orrectangular, for example, and which form the ohmic connections to the 50Ohm transmission line, and subsequently define the lower plate of thecapacitors supporting the electromagnetic coupling to the upper surfaceof the subject microwave device. The bottom signal connection structures37A, 37B, have width dimensions, w₂, in a range of about 0.356 mm to0.457 mm, preferably 0.406 mm, and length dimensions, l₂, in a range ofabout 0.304 mm to 0.406, preferably 0.356 mm. The respective signalconnections 37A, 37B are surrounded by the electrically insulatingisolation areas 38A, 38B. The isolation areas 38A, 38B preferably definea gap having dimensions in a range of about 0.203 mm to 0.305 mm,preferably 0.254 mm, between the peripheral edges of the respectivesignal connection structures and peripheral portions of the ground plane39. The signal connections 37A, 37B are also spaced a distance d₂ awayfrom the terminal, peripheral edges of the bottom surface 32 b and donot extend over the sides 32 c, 32 d of the filter substrate 32.Preferably, the distance d₂ is in a range of 0.00 mm to 0.076 mm, morepreferably 0.050 mm. The locations of the signal connections 37A, 37B onthe bottom surface 32 b positionally correspond to (i.e., are coincidentwith) the locations of the respective RF input and output connections33A, 33B on the upper surface 32 a.

Suitable substrate materials include those typically employed in thedesign of planar, mm-Wave, surface mount filters, and include Alumina,or other ceramic materials which are rigid, have a smooth surfaceroughness of ˜0.1 um or better, have a low loss tangent, preferably lessthan 0.001 at the frequency of use, and which exhibit dielectricconstant temperature stability, preferably less than 50 ppm/° C., suchas materials from Dielectric Laboratories, Inc., known as PG and CF, forexample. In the context of the present invention, the substrate materialpreferably has a dielectric constant in a range of 9 to 25. Commerciallyavailable materials are generally available in thickness of 0.203 mm to0.635 mm, for example. The thickness t of the filter substrate 32, inconjunction with the dielectric constant of the substrate material, isimportant with respect to achieving the desired filter functionality atthe design operating frequency and performance in connection with theassociated matching structures, as known in the art. The preferredthickness in the context of the present invention is 0.254 mm. Filtersubstrate material parameters, including thickness and dielectricconstant, must be selected based on the intended performancerequirements of the filter, in view of the known industry standards fora particular frequency range. Adjustment of the inventiveelectromagnetic coupling is accomplished by adjusting the dimensions ofthe input and output structures 33A and 33B.

The dimensional ranges noted above are important to ensure thateffective capacitive coupling is achieved through the thicknessdirection t of the filter substrate 32 between the signal connections37A, 37B on the bottom surface 32 b of the filter substrate and RFinput/output 33A, 33B (and the plurality of filter components) on theupper surface 32 a of the filter substrate without providing any directcoupling through vertical metallic conductive structures. In thatmanner, the present invention eliminates the presence of verticalconductive structures within the filter at the input and the outputthereof.

WORKING EXAMPLE

FIGS. 5A-5C represent a filter structure according to a working exampleof the present invention, and correspond to the general structure shownin FIGS. 3A-3C, but include the specific dimensional attributes of theworking example. Like components have been designated with likereference numbers, and repeat descriptions of like components areomitted.

The band pass filter 50 includes RF signal input and output structures53A, 53B, impedance matching structures 54A, 54B and filter sections55A-55D on the upper surface 52 a of the filter substrate 52. The filtersubstrate 52 is made of a dielectric ceramic composition having adielectric constant of 13. The impedance matching structures of theworking example specifically include two pairs of open circuitterminated transmission lines, stubs, placed strategically between theRF signal input and output structures 53A and 53B. The bottom surface 52b of the filter substrate 52 includes the signal connection structures57A, 57B, the electrically insulating isolation areas 58A, 58B and theground plane 59. The specific dimensions of the respective portions areshown in FIGS. 5A and 5B.

FIG. 5D shows the insertion loss and return loss results of the filter50 according to the working example, which were achieved by mounting thefilter 50 shown in of FIG. 5A-5C onto a test circuit board (e.g., 0.010inch thick microwave circuit board material) using solder reflowtechniques, and standard two-port s-parameter measurements wereperformed.

FIG. 5D shows that the filter 50 according to the working exampleexhibited the desired filter performance characteristics in the desiredfrequency range without direct ohmic contact between the signalconnection structures 57A, 57B on the bottom surface 52 b of the filtersubstrate 52 and the RF input/output structures 53A, 53B on the uppersurface 52 a of the filter substrate 52. It can be seen from theinsertion loss plot and the return loss plot from 30 GHz to 50 GHz thereis no evidence of spurious modes being launched.

The present invention thus provides an effective and novel solution tothe drawbacks associated with conventional surface mounted band passfilters, which was heretofore unknown in the art. While the presentinvention is described primarily in the context of high frequency bandpass filters, it should be noted that the specific coupling mechanismembodied by the present invention can also be applied in connection withother high frequency, passive and active RF devices.

For example, it should be understood by skilled artisans that thepresent invention is also applicable with respect to both passive andactive RF circuits with one or more RF ports, including but not limitedto power dividers, couplers, mixers, and frequency multipliers, etc. Forinstance, FIG. 6 shows an example of an electrical schematicrepresentation a package for an active high frequency, narrow banddevice according to another aspect of the present invention. Electricalpower is provided to the active components by direct ohmic contact,while capacitive coupling between the bottom signal connectionstructures and the RF input/output of the active device is achievedaccording to the present invention.

One skilled in the art would be able to modify such devices, based onthe disclosure in the present application, to include a coupled surfacemount transition, rather than vertical conductive structures, takinginto account the necessary design parameters of the specific intendeddevice.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawings, itwill be understood by one skilled in the art that various changes indetail may be effected therein without departing from the spirit andscope of the invention as defined by the claims.

What is claimed is:
 1. A high frequency band pass filter with a coupledsurface mount transition, comprising: a dielectric filter substratehaving a first surface and an opposed second surface; circuit connectionelements defining an input element and an output element provided on thefirst surface of the filter substrate and spaced a distance d fromrespective terminal edges of the first surface of the filter substrate;electronic filter components provided on the first surface of the filtersubstrate and extending along a longitudinal extension axis of thefilter substrate from a first point proximate a first end of the filtersubstrate to a second point proximate a second end of the filtersubstrate; impedance matching structures provided on the first surfaceof the filter substrate and interposed between the input element and theelectronic filter components and between the output element and theelectronic filter components; at least one protrusion integrallyconnected to each impedance matching structure and extending to aposition between the first and second points; and signal connectionelements provided on the second surface of the filter substrate inlocations that positionally correspond to respective positions of theinput element and output element on the first surface of the filtersubstrate, the signal connection elements respectively separated from aground plane on the second surface of the filter substrate by anelectrically insulating isolation area, and being spaced a distance d₂from respective terminal edges of the second surface of the filtersubstrate; whereby the respective signal connection elements on thesecond surface of the filter substrate are capacitively coupled, througha thickness direction of the filter substrate, to a respective one ofthe input and output elements on the first surface of the filtersubstrate without the presence of any vertical conductive structureswithin the filter substrate at the circuit connection elements.
 2. Thehigh frequency band pass filter with a coupled surface mount transitionaccording to claim 1, wherein the filter substrate comprises a ceramicmaterial having a dielectric constant in a range of 9-25.
 3. The highfrequency band pass filter with a coupled surface mount transitionaccording to claim 1, wherein the input and output elements have a widthdimension in a range of 0.254 mm to 0.356 mm and a length dimension in arange of 0.254 mm to 0.356 mm.
 4. The high frequency band pass filterwith a coupled surface mount transition according to claim 1, whereinthe signal connection elements have a width dimension in a range of0.356 mm to 0.457 mm and a length dimension in a range of
 0. 304 mm to0.406 mm.
 5. The high frequency band pass filter with a coupled surfacemount transition according to claim 1, wherein the distance d is in arange of 0.00 mm to 0.127 mm.
 6. The high frequency band pass filterwith a coupled surface mount transition according to claim 1, whereinthe distance d₂ is in a range of 0.00 mm to 0.076 mm.
 7. The highfrequency band pass filter with a coupled surface mount transitionaccording to claim 1, wherein the protrusion extends in parallel to thelongitudinal extension axis of the substrate.
 8. A high frequency bandpass filter with a coupled surface mount transition, comprising: afilter substrate; circuit connection elements defining an input elementand an output element provided on a first surface of the filtersubstrate; electronic filter components provided on the first surface ofthe filter substrate and extending along a longitudinal extension axisof the filter substrate from a first point proximate a first end of thefilter substrate to a second point proximate a second end of the filtersubstrate; impedance matching structures provided on the first surfaceof the filter substrate between the electronic filter components and therespective input and output elements; at least one protrusion integrallyconnected to each impedance matching structure and extending to aposition between the first and second points; and signal connectionelements provided on an opposed second surface of the filter substrate,in locations that positionally correspond to respective positions of theinput and output elements on the first surface of the filter substrate;whereby the respective signal connection elements on the second surfaceof the filter substrate are capacitively coupled, through a thicknessdirection of the filter substrate, to a respective one of the input andoutput elements on the first surface of the filter substrate without thepresence of any vertical conductive structures within the filtersubstrate at the circuit connection elements.